Certain applications require the use of double-walled tank containers. In this case, an inner container is more or less completely enclosed by an outer container. These designs are necessary when the container needs to be extremely leak-proof, such as, for example, when the interior plate is brittle and the inner tank requires a high degree of protection against exterior impacts, or needs to be completely protected by a liquid temperature equalization medium. The leak-proof character often needs to be further increased by filling the space between the outer and inner tank with a non-hazardous test liquid thus revealing possible leaks in both the inner as the outer tank.
It is expedient that the outer containers of such tank containers can be incorporated in proven and standardized frame constructions customary for single-walled containers. Ring saddle mountings, such as described in DE 32 12 696 C2, have proven to be worthwhile in the field of tank containers. In this design, the tank is connected with the front frames via the vaulted dished ends of the tank. This construction enables the stress between the tank and the frame, which occurs during handling and transportation of the tank containers, to be completely imparted. Other connections between the tank and the frame are generally not necessary.
FIG. 7 shows a known design of a head ring saddle mounting on a double-walled container, whereby a front ring (12′) runs through the exterior bottom plate (8′, 8″) and is welded to the interior bottom plate (3′). This requires separating the exterior dished end and running a piece (8′) around the interior bottom plate (3′) back to the front ring (12′), as well as mounting an exterior bottom piece (8″) in the front ring (12″). This procedure is unsatisfactory from a production viewpoint and unsuitable for inner containers with a brittle interior bottom plate since the stresses from transportation and handling directly work on the tank plate covered with the coat. Increasing the wall thickness of the entire inner tank, or at least the dished ends of the inner container, can offset this. This would increase the weight of the tank considerably.
Furthermore, this design does not guarantee that the container will be leak-proof and increases the production cost. The head ring (12′) needs to be interrupted in the area where it is connected with the interior dished end in order to enable the hollow space (10′) inside the head ring to interconnect with the hollow space (10′) outside the head ring, and to allow a leakage detector liquid to run through it. Furthermore, there is a risk that a leak (3″) in the area of the welding between the head ring (12′) and the interior dished end is not shown because possible double sheet metal plating (12″) in the head ring might cause the leak to seep out through the exterior bottom plate (8′, 8″) without activating the leakage detector.